Distributed sensor networks utilize a set of sensors performing measurements across time and space to gather information about their environment. The sensors typically use wireless communication (e.g., radio transmission) to send their measured data to a central computer system, which accumulates the data and builds it into a larger picture. In some distributed sensor network systems, the sensor nodes are distributed in space randomly or without knowledge of their position or sensor nodes are not stationary (e.g., are able to move or are attached to an object that moves). Distribution of sensors in this way can be of considerably lower cost than ensuring precise sensor positioning, and data produced by sensors distributed in this way can still be valid and useful. For some applications, random sensor distribution is acceptable, but it is advantageous to know precisely the eventual sensor locations or the location of sensors that move.
Some systems (e.g., global positioning (GPS) systems) accomplish localization of nodes using time of flight measurements and clock systems on each node that are very accurate and synchronized precisely. In systems designed for low cost and low node power consumption, these methods are not feasible.